Picture this American scene: Two friends rolling down I-40 somewhere outside Nashville, singing out the open window. The backseat is a jumble of guitars, boots, takeaway plates from a roadside BBQ, and paperback books.

The friends are Anaïs Mitchell and Jefferson Hamer, two songwriters who co-arranged a selection of epic old folk songs from across the Atlantic for their current release “Child Ballads.” For Mitchell, this recording comes on the heels of 2010’s “Hadestown” and 2012’s “Young Man in America.” Both albums are big on story; the first is a folk opera, while the second was described by the Independent on Sunday as “an epic tale of American becoming.”

The two will perform at the Narrows Center for the Arts on Sunday, April 14 at 8 p.m. Doors open at 7 p.m. Eamon O’Leary will open the performance.

Hamer began his career with the Colorado roots rock band Great American Taxi, but moved to New York in 2008 to pursue songwriting and a passion for Irish traditional music.

Mitchell and Hamer quickly discovered their shared love of Celtic and British Isles ballads, especially the classic folk albums of the 1970s and made a plan to arrange and record some of their favorites together. But what began as a whimsical side project evolved into a serious collaborative endeavor spanning several years, three separate recording attempts, and a whole lot of cutting room floor as the pair navigated their way through a centuries old tradition.

There is something about the trans-Atlantic conversation — Americans tackling Celtic and British music and vice-versa — that is perennially inspiring to artists on both sides of the pond.

“The language, and the music, is both familiar and exotic at the same time,” says Mitchell. “It’s inspiring, and it’s a rabbit-hole. It’s no wonder it took us so long.”

“I’m not sorry it did,” Hamer reflects. “I’d say the songs worked on us as much as we worked on them.”